Thermally insulated storage vessels



Dec. 8, 1959 A. G. MONROE THERMALLY INSULATED STORAGE VESSELS Filed Dec.1'7, 1958 Inventor 4041/ 6656018} you f y QM M Attorney United StatesPatent 2,916,179 THERMALLY INSULATED STORAGE VESSELS Adam GregoryMonroe, Cheam, England, assignor to The British Oxygen Company Limited,a British com- P y Application December 17, 1958, Serial No. 781,158

Claims priority, application Great Britain January 13, 1958 3 Claims.(Cl. 220-15) This invention relates to thermally insulated storagevessels for the storage of liquids at temperatures substantially aboveor substantially below atmospheric temperature. The invention isparticularly applicable to the storage of liquids having a boiling pointsubstantially below atmospheric temperature, for example, liquid methaneand liquiefied atmospheric gases such as liquid oxygen and liquidnitrogen, and for the sake of clarity the invention will be describedwith reference to the storage of such liquids. It will be appreciated,however, that the same considerations will apply to the storage ofliquids at temperatures substantially above atmospheric temperature.

In order to reduce the evaporation losses of liquids, the boiling pointsof which lie substantially below atmospheric temperature, duringstorage, the liquids are usually stored in thermally insulated vesselscol prising an inner container for the liquid and an outer shellsurrounding and spaced from the container, the interspace being filledwith a thermal insulation material of fibrous or cellular structure.

It has been observed that the insulation properties of the insulatingmaterial deteriorate with time for various reasons.- If the innercontainer for the liquid is subjected to temperature fluctuations, itsoveralldimensions vary in accordance with the thermal dilation. Thus,when warming up or cooling down to or from ambient temperature, themovements of the inner container, which is usually, of metal, aretransmitted to the insulation surrounding it and have a deleteriouselfect'thereon.

When fibrous insulation is used to fill the interspace, the insulation,although originally resilient, gradually becomes less so, owing to thethermal movements of the inner container, which cause the individualfibres to become felted together. Further deterioration of theinsulation may then be caused by the ingress of moisture to theinterspace and in the case of the storage of liquid at temperaturessubstantially below ambient its subsequent solidification within theinterstices of the insulant. The average thermal conductivity of amixture of fibrous insulant and ice is substantially higher than that ofthe dry fibrous insulant.

A mixture formed of fibres and ice is quite'rigid and, once compressedby thermal dilation of the inner container, retains its smaller volume.As a result, on subsequent contraction of the inner container, a voidspace is formed between the insulation and the container which in theextreme case where moist air has fairly free access to the intersticialspaces in the insulant, would be filled with a layer of ice. It is thusessential to maintain the resilient properties of the insulant and toavoid the formation of voids.

When the cellular type of insulation is used, deterioration ofinsulating properties also takes place for the following reasons. In thefirst place, the majority of cellular insulating materials are friableand attrition of the insulant takes place as a result of thermalmovements of the inner container. The broken-down par- "ice 2 ticles ofthe insulant agglomerate andform a, porous body, which has asubstantially higher bulk density than the original material and acorrespondingly higher thermal conductivity. It further has practicallyno resilience, forming solid plugs when compressed. Again, when ingressof moisture takes place into the interspace, water may be absorbed bythe powdered insulant or even chemically combined therewith, as is thecase, for example, with basic magnesium carbonate where the resultantmixture is very similar to and behaves like cement;

It will be seen, therefore, that thermal dilation movements of the innercontainer may not be accommodated within cellular insulating material,either because the latter has reached its final bulk density and isincompressible, or because it has formed a cement. Consequently, theouter shell of the storage vessel, which is as a rule considerablythinner than the inner container, will be subjected to excessiveinternal pressure and may be perforated.

It is an object of the present invention to provide a thermallyinsulated vessel for the storage of liquids at temperaturessubstantially above or below atmospheric temperature, and particularlyfor the storage of liquefied gases, the boiling points of which aresubstantiallybelow atmospheric temperature, in which thermal dilationmovements of the inner container are accommodated within the insulationspace in such a manner that no deterioration of the insulatingperformance takes place and the outer shell protecting the insulation isnot mechanically affected in any way.

According to the present invention, in a storage vessel for the storageof a liquid at a temperature substantially above or substantially belowatmospheric temperature comprising an inner container for the liquid,and an outer shell surrounding and spaced from the inner container,theinterspace being filled with thermally insulating material, thermalmovements of said inner container are transmitted to and absorbed by apreformed body of resilient material forming a part of said thermallyinsulating material.

The thermal movements of the inner container may be transmitted to thepreformed resilient material by a body of thermally insulating materialin the form of substantially spherular particles freely movable withrespect to one another and in contact both with a part of the innercontainer liable to thermal movement and with the resilient material.

It will be appreciated that in any given case, the particular resilientmaterial and the particular spherular material used must be selectedwith due regard to the temperature of the liquid being stored.

One arrangement in accordance with the invention is illustrated in theaccompanying drawing which shows a sectional side view of a storagevessel according to the invention suitable for the storage of liquefiedgases of boiling point substantially below atmospheric temperature, forexample, liquid oxygen, liquid nitrogen and liquid methane. The storagevessel comprises a substantially cylindrical inner container 1 for theliquefied gas made of a material the mechanical properties of which donot deteriorate at low temperatures, such as, for example, austeniticstainless steel, copper and its alloys, and aluminum and its alloys. Theinner container 1 is surrounded by and spaced from an outer shell 2which is of thinner material and serves merely to contain the insulatingmaterial. It does not contribute to the support of the innercontainer 1. This is suspended within the outer shell 2 by means ofsupporting members. These are shown in the drawing as chains 3 but mayequally be rods or wires. Each of the chains 3 is connected at one endto a supporting element 4 mounted on the outer wall of the container 1and at the other to a main structural element supporting the storagevessel indicated at 5. The inner container 1 is therefore free to expandand contract in a vertical direction.

The thermal insulation is contained within the interspace between theinner container 1 and the outer shell 2. This insulation is in threelayers. The lowest layer 6 filling the bottom of the interspace consistsof substantially spherular particles of insulating material, of averagediameter not greater than /8 inch. The spherules may be of anysubstantially non-friable material having a low thermal conductivity,for example, polytetrafluoroethylene,.nylon, polyvinyl chloride, glass,or slag.

I Directly above the layer 6 of spherular material and in contacttherewith is a layer 7 of resilient insulating material, such as, forexample, expanded polyvinyl chloride, preformed as a hollow cylindricalbody of wall thickness equal to the Width of the interspace. This layeracts as a centering device for the inner container 1, as a sealingdevice for insulating material placed above it, and owing to itsresilience, it accommodates any dis placement movements of theinsulation above or below it.

The remainder of the interspace above the layer 7 of resilient materialis filled with conventional insulation 8 for low temperature equipment,such as slag wool, mineral wool, expanded aluminium-magnesium silicateknown as brelite or perlite, silica aerogel, diatomaceous earth, or amicaceous earth such as vermiculite.

In operation, when the inner container 1 is warmed or cooled by theremoval from or introduction into it of a liquefied gas, the containerwill expand or contract respectively. When the container expands, forceis exerted on the bottom layer 6 of the insulant. When under stress the-body of spherular particles behaves like a liquid, and the forceexerted on the surface of the layer 6 by the expanding container istransmitted and distributed uniformly within the body of spherularparticles with very low frictional losses and negligiblecompressibility. As a result, the spherular particles are forceddownwardly by the expansion of the inner container and rise near thecircumference of the outer shell and compress the resilient layer 7.

Similarly, contraction of the inner container 1 causes an upwardmovementof its lower end. The resultant free space directly under the containerwill befilled by the'spherular particles moved by the expansion of theresilient layer 7 when the thrust exerted by the dilated container isreleased.

Thus in both the expanded and contracted condition of the innercontainer 1, no voids are present in the insulation, nor is the outershell 2 stressed. It will be appreciated, of course, that in filling theinsulation space, which will normally be carried out with the container1 empty and consequently at atmospheric temperature, it is necessarythat the resilient layer 7 is compressed against the layer 6 ofspherular material to an extent sufficient to ensure that when thevessel is cooled to the desired storage temperature, and the innercontainer 1 is consequently fully contracted, the spherular materialcompletely fills the interspace below the resilient layer 7, while thelatter is uncompressed or only slightly compressed.

I claim:

1. A storage vessel for the storage of a liquid at a temperaturesubstantially different from atmospheric temperature comprising an innercontainer for the liquid, an outer shell surrounding and spaced fromsaid inner container to define therewith an interspace, a body ofthermally insulating material in the form of spherular particles freelymovable with respect to one another filling the bottom of saidinterspace, a body of conventional thermal insulation filling the upperpart of said interspace, and a preformed body of resilient materialwithin said interspace separating and in contact with said first andsecond mentioned bodies of thermally insulated material.

2. A storage vessel according to claim 1 wherein said spherularparticles are made of a material selected from the group consisting ofpolytetrafluoroethylene, nylon, polyvinyl chloride, glass and slag.

3. A storage vessel according to claim 1 wherein said resilient materialis expanded polyvinyl chloride.

References Cited in the file of this patent UNITED STATES PATENTS1,463,498 Burgess July 31, 1923 I 1,866,517 Heylandt July 5, 19321,979,221 Dano Oct. 30, 1934 2,110,470 Norton Mar. 8, 1938 2,481,664Hemp Sept. 13, 1949

